page_title: Headlamp
section_title: High-intensity discharge (HID)
hierarchical_section_title: Headlamp / Light sources / High-intensity discharge (HID)
caption_attribution_description: English: 2009 Lincoln MKS: Adaptive Headlamps with Standard High-Intensity Discharge (HID) Lamps enhance nighttime visibility by illuminating more of the road and reducing glare from oncoming traffic. Sensors monitor vehicle speed and steering wheel input engaging electric motors that pivot the left headlamp up to five degrees and the right headlamp up to 15 degrees to increase the driver’s field of vision.
context_page_description: A headlamp is a lamp attached to the front of a vehicle to illuminate the road ahead. Headlamps are also often called headlights, but in the most precise usage, headlamp is the term for the device itself and headlight is the term for the beam of light produced and distributed by the device.
  Headlamp performance has steadily improved throughout the automobile age, spurred by the great disparity between daytime and nighttime traffic fatalities: the US National Highway Traffic Safety Administration states that nearly half of all traffic-related fatalities occur in the dark, despite only 25% of traffic travelling during darkness.
  Other vehicles, such as trains and aircraft, are required to have headlamps. Bicycle headlamps are often used on bicycles, and are required in some jurisdictions. They can be powered by a battery or a small generator like a bottle or hub dynamo.
context_section_description: High-intensity discharge lamps (HID) produce light with an electric arc rather than a glowing filament. The high intensity of the arc comes from metallic salts that are vaporized within the arc chamber. These lamps have a higher efficacy than tungsten lamps. Because of the increased amounts of light available from HID burners relative to halogen bulbs, HID headlamps producing a given beam pattern can be made smaller than halogen headlamps producing a comparable beam pattern. Alternatively, the larger size can be retained, in which case the xenon headlamp can produce a more robust beam pattern.
  Automotive HID may be called "xenon headlamps", though they are actually metal-halide lamps that contain xenon gas. The xenon gas allows the lamps to produce minimally adequate light immediately upon start, and shortens the run-up time. The usage of argon, as is commonly done in street lights and other stationary metal-halide lamp applications, causes lamps to take several minutes to reach their full output.
  The light from HID headlamps can exhibit a distinct bluish tint when compared with tungsten-filament headlamps.
caption: HID projector low beam headlamp illuminated on a Lincoln MKS
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